Chuck is popularly used to hold the wafer to be processed. For example, in the plasma chamber used to perform the plasma process, such as CVD, PECVD and etching, the chuck is used to hold the wafer and apply electric voltage for attracting ions from the plasma to the wafer. For example, in the ion implanter, the wafer is held by the chuck and the ions are delivered to the wafer. However, in some instances an amount of charges may be accumulated on the processed wafer, especially on the frontside surface of the implanted wafer. Some popular causes of charge accumulation are listed as below: the ions may be not properly neutralized, even not neutralized, before the ions react with the wafer, the plasma or related reactive gas(es) may directly contact with both sides of the wafer, and the wafer may be not fully grounded through pins that connect the backside surface of the wafer to the ground due to improper installation, contamination, insulated layer on the backside surface and so on. No matter how the charges are accumulated and/or how the amount of the charges is varied, the existence of non-zero charges unavoidably induces some disadvantages. For example, the devices formed on and/or in the wafer may be damaged, and the wafer may be broken during the process of moving processed wafer away the chuck (such as electrostatic chuck) holding the wafer.
Some technologies have been proposed to monitor (or viewed as sense or detect) the charges on the wafer, for example, but not limited to, the following US patents: U.S. Pat. Nos. 7,038,223, 7,112,810, 7,675,730 and 8,111,499. In short, U.S. Pat. No. 7,112,810 disposes the charge sensor adjacent to a surface of the wafer for monitor charges on the wafer surface, U.S. Pat. No. 8,111,499 disposes a residual charge sensor along a discharging path to sense a residual charge discharging from the wafer via the discharge path, U.S. Pat. No. 7,676,730 uses an electron beam gun to inject E-beam above the top surface of the wafer and then monitor how the trajectory of the E-beam is affected by any charge buildup, and U.S. Pat. No. 7,038,223 uses the arrays of charge-sensing probes for sensing charges. Besides, just for example, the article “Proc. Frontiers in Low Temperature Plasma Diagnostics IV, Rolduc, Netherlands, March 2001, P.230” also discloses that the charging monitor only may be done after the plasma process. However, it is still a field to be improved about how to achieve wafer charge monitoring in a real-time manner with simple hardware and simple operation, even with less population and less noise.
Therefore, it is required to provide new and improved apparatus and/or method for monitoring the charges appeared on the wafer held by chuck, especially on the processed wafer.